A component comprising a luminescence conversion element is known, for example, from Pre-Published German Patent Application WO 97/50132. It comprises a semiconductor chip that emits primary radiation when in operation, and a luminescence conversion element by means of which a portion of the primary radiation is converted into light of another wavelength. The resulting optically perceptible radiation from the LED light source is created by overlapping of the two radiations, so that light sources particularly emitting white light can be produced by this means.
The luminescence conversion element ordinarily comprises a phosphor embedded in a matrix material. Suitable for use as phosphors are, for example, inorganic phosphors, such as garnets doped with rare earths (particularly Ce), or organic phosphors, such as perylene phosphors. Further suitable phosphors are cited for example in WO 98/12757, whose content in that respect is incorporated herein by reference.
To obtain particularly good mixing of the radiation and thus a resultant radiation that is largely chromatically homogeneous, it is advantageous to apply the phosphor directly and evenly to the chip surface, so that the luminescence conversion element causes the smallest possible differences in the path length of the primary radiation. For example, the luminescence conversion material can be applied to the surface of the LED chip, in the form of a thin, homogeneous layer of constant thickness, even before the chip is mounted on a leadframe and electrically contacted. The application of thin layers can be performed in a number of ways and is suitable in particular for the simultaneous production of multiple LED light sources from LED chips disposed in a wafer composite along with a multiplicity of similar chips. This approach also, insofar as possible, prevents color fluctuations of the LED light sources due to sedimentation of the conversion materials.
However, a thin layer cannot be applied in a straightforward manner if the LED chip used has electrical contact layers on its front side (that is, the side facing in the direction of radiation), as is usually the case, for example, with GaN-based diodes on an SiC substrate. Care must be taken to preserve electrical contactability in coating the surfaces of such LED chips.